Electrical fuse link



Nov. 9, 1937. o. H. JUNG El AL ELECTRICAL FUSE LINK Filed April 16, 1934cam Ma Patented Nov. 9, 1937 UNITED STATES ELECTRICAL FUSE LINK Oscar H.Jung and Paul E. Heflelilnger, Mllwaukee, Wia, alsignorl to 'lrloo FuseMfg. 00.,

Milwaukee, Wis.

Application April 18,

'1 Claims.

This invention pertains to electrical fuse links of either the renewableor non-renewable type, and is directed particularly to links providedwith a time lag for overloads of comparatively brief duration.

Links having a time lag in their fusing period are well-known in theart, and therefore it is considered unnecessary to discuss their purposeor mode of operation, other than that the links now in common useprovide for a time lag by either the attachment of additional metal tocertain portions of the fuse, or by increasing the metallic crosssectional area of certain portions of the fuse in various ways, with theresult that a greater amount of metal is volatilized upon the blowing ofthe fuse links on short circuits, which is both highly detrimental tothe fuse casing, and creates a serious explosive hazard.

The present invention has primarily for its object to overcome theforegoing objects by the provision of a fuse link having a practicalcommercial time lag, which is not detrimental to the short circuitcharacteristics of the link, and which reduces the explosive efiect uponthe fuse casing to a minimum, thus eliminating resultant hazard, andmaterially reducing the cost of manufacture of the casing, in that alighter construction is permissible.

Incidental to the foregoing, a more specific object of the presentinvention resides in coating a fuse link with an electricalnon-conducting material, but having heat-conducting properties, toincrease the inherent time lag of the link without increasing thequantity of metal to be volatilized upon short circuit fusing.

A still further object is to provide a fuse link having the foregoingcharacteristics, in which its potential fusing portion, or portions, arepacked in a suitable powdered material, which serves to both quench andde-ionize the explosive are upon fusing, and further increase the timelag of the link.

With the above and other objects in view, which will appear as thedescription proceeds, the in- 45 vention resides in the novelconstruction, combination, and arrangement of parts, substantially ashereinafter described, and more particularly defined by the appendedclaims, it being understood that such changes in the precise embodimentof the herein disclosed invention may be made as come within the scopeof the claims.

In the accompanying drawing is illustrated one complete example of theplrwsical embodiment of the present invention constructed according tothe best mode so far devised for the practical application of theprinciples thereof.

In the drawing:-

Figure 1 is an elevation of a fuse link constructed in accordance withone form of the present inven- 60 tion, the powder tube being shown insection.

1984, Serial No. 720,770

Figure 2 is a longitudinal section taken on the line 2-2 of Figure 1.

Figure 3 is a transverse section taken on the line 3-4 of Figure 2.

Referring now more particularly to the accompanying drawing, the numeralI designates a fuse link of that type commonly known as a drop-out link,and comprising a fusible section 2 having end attaching terminals 3secured thereto. Here it is to be understood that the end terminals Imay be formed of the same material and integrally with the fusiblesection 2. However, when it is desired to reduce the resistance of thelink, the separate terminals 3, formed from copper or other highconductive material of low resistance, are employed. In the presentinstance, the terminals 3 are provided with tongues 4, which passthrough suitable openings in the ends of the fusible section 2, and arecrimped over the same, the terminals being further soldered, or welded,to the ends of the fusible section 2, in order to secure the desiredcontact.

In a drop-out type of link, such as illustrated, the fusible section 2is provided with one or more enlarged portions 5,"'having adjacentrestricted potential fusing portions 6. Naturally, the greatestresistance. in a fusing link occurs centrally of the ends of the link.However, in the type of link shown, the central portion 5, being ofconsiderably greater area than the adjacent restricted portions 6,requires a greater period of time to become heated to the fusing pointthan the restricted portions, and hence fusing will occur at therestricted portions, causing the intermediate portion to drop out andprevent subsequent arcing, which occurs in links having only onepotential fusing portion.

From the foregoing, it will be readily appreciated that a drop-out linkof low capacity requires only two space restricted portions. However, inlarger capacity fuses any number of restricted portions may be provided,such as illustrated in the present instance, and while a link of thistype may fuse at only one point in instances of light overload andresultant slow heating of the link, in instances of a dead short thelink will generally fuse at all of the restricted portions. It isfurther well known that a link of the foregoing type provides a timelag, inasmuch as the enlarged intermediate portions 5 absorb and conductthe heat away from the potential fusing portions, thus requiring aprolonged period of overload to effect fusing. However, the time lagthus acquired is not sufllcient to be commercially practical, and,therefore, in order to increase the time lag, it is customary to attachadditional metallic plates to the enlarged portions 5, with the resultthat the time lag is materially increased, but at the same timeconsiderable additional metal is added to the link, and a greater amountis volatilized upon fusing, thus increasing the explosive effect, whichis not only detrimental to the fuse casing, but also creates a seriousfire hazard. To meet this situation, commercial fuses now on the marketare made of exceedingly heavy material, and require rigid attachment ofthe end caps' to thecasing, thus materially increasing the cost ofmanufacture.

To eliminate the foregoing objections, the present invention providesfor the most practical commercial time lag by coating the intermediateportion of the link with any suitable non-metallic material i2,characterized by its ability to conduct heat, and at the same timeact'as an electrical non-conductor, and inasmuch as the materialemployed has greater conducting properties than absorption properties,the same rapidly conducts the heat from the enlarged portions 5, whichin turn conduct the heat from the restricted potential fusing portion 6,and because of the relatively large area of contact between the coatingand link, with resultant maximum radiating surface of the coating, amaximum time lag is obtained without affecting the short circuitcharacteristic of the link. While the coating i2 may be formed fromvarious ingredients, one formula which has been found most satisfactorycomprises a mixture of refractory cement, and either borax or sodiumbicarbonate.

In forming the present link, a coating oi. plastic material is appliedto the desired surfaces, leaving the edges free, inasmuch as actualtests have demonstrated that an arc shield is unnecessary in the presentlink. It has further been found that the amount or thickness of coatinghas practically little or no effect upon the time lag, inasmuch as theaction that takes place is one of conducting the heat away from the linkrather than absorption of the same. Therefore, little or no care orskill is required in applying the coating.

Attention is further directed to the fact that in applying coating in aplastic state, it inherently assumes the form illustrated in thedrawing, in which the greatest thickness occurs at the center or hottestpart of the surface coated, from which the coating tapers off to theedges of the link, with the result that amaximum desired conduction, andtherefore uniform cooling of the coated areas, takes place. 1

In the form of the invention illustrated and described, only theintermediate enlarged areas of the link are coated, leaving thepotential fusing portions free.

To further increase the time lag period, and at the same time quench thefusing arc, it is proposed to encase the intermediate fusible portion ofthe link in a suitable powdered material capable of breaking up anddeionizing the arc, with resultant quenching of the same. Obviously,inasmuch as such powdered material must have some absorptive capacity,heat conducted away from the potential fusible portions by the enlargedcoated portions will also be absorbed by the powder, resulting infurther increasing the time lag inherent in the link itself.

Also, it has been found that by coating a fuse link of any type in themanner described, with material characterized by its ability to bebroken up by the heat of the fusing arc, and produce a turbulent blastof neutral gases, such gases act to effectively de-ionize and quench thearc, which is desirable for reasons heretofore set forth.

One method by which the foregoing is accomplished resides in theprovision of a'flbrous tubular casing I, the ends of which arereinforced by the metallic bands 8 inserted into the tube. Slotted endcaps 8, which receive the terminals 3, are then crimped over the outerends of the tube to provide a comparatively rigid and inexpensivehousing for the quenching powder 9, with which the tube is filled beforeclosing. To further obstructthe-passage of gases from the cartridge thusformed, a layer of 'fiocculent or fine comminuted material H, such asasbestos or the like, is positioned at the ends of the tube surroundingthe terminals adjacent the slots in the end caps 3. To further securethe end caps 8' upon the tube 1, and also to prevent longitudinalshifting of the link within the cartridge, the terminals 3 may beprovided with struck-out nibs III which engage the outer faces of theend caps.

From the foregoing explanation, considered in connection with theaccompanying drawing, it will be readily seen that an exceedinglysimple, inexpensive, and efliclent fuse link has been provided, whichaffords a maximum practical time lag with a minimum quantity of metal,thus materially reducing detrimental effects of the fusing explosionupon the fuse shell, and eliminating entirely possible fire hazard.

We claim:--

1. A fuse link provided with spaced potential fusible portions and anenlarged intermediate area, the surface of the intermediate portionbeing coated with a material which is an electrical non-conductor, andat the same time a heat conductor, the thickness of the coating beinggradually reduced to nothing toward the edges of the .coated area.

2. A fuse link having a potential fusing section, a portion of which iscoated with a non-conducting material, said coating being graduallyreduced toward the edges of the coated area so as to expose the edge ofthe fusible link.

3. A fuse link having spaced intermediate portions of uniform crosssection coated with a nonmetallic substance, the coating being graduallyreduced in thickness toward the edges of the coated area so as to exposethe edges of the fusible link.

4. A fuse link comprising intermediate its ter- J minals a series ofcoated areas, the coated poring gradually reduced toward the edges ofthe coated area so as to expose the edges of the link.

6. A fuse link comprising spaced potential fuse sections and an enlargedintermediate section therebetween having a series of non-metallic coatedareas of substantial uniform cross section intermediate its terminals,the coating being gradually reduced toward the edges of the coated areaso as to expose the edges of the link.

'7. A fuse link comprising a series of potential fusible sections and aplurality of enlarged intermediate sections being coated with anon-conducting material, said coating being gradually reduced toward theedges of the coated area so as to expose the edges of the fusible link.

' OSCAR H. JUNG.

PAUL E. HEFFEIJ'INGER.

